As is generally known in the industry, the operational costs of conventional water heaters account for approximately ten-percent to twenty-percent or more of an average household's annual energy expenditures. In this regard, the cost to operate a conventional gas or electric water heater (i.e., a storage tank-type) in a typical household averages between $300 and $600 annually, respectively (although the costs can be much more in larger homes and commercial buildings).
Although a variety of water heater types are known and used throughout the world, in the United States, acceptance of water heater types, other than storage tank-types, has not been widespread. Thus, the vast majority of water heaters used in the United States are of the storage tank variety.
A conventional storage tank-water heater includes a water storage reservoir in which water is heated and then stored for use by the household. In such a water heater, there is cold water inlet at the bottom of the storage tank and a hot water outlet located at the top of the storage tank. In a gas fueled storage tank-type water heater, in order to heat the water within the storage tank, a burner is provided which normally burns natural or propane gas. Conversely, in a typical electrically powered storage tank-type water heater, electric current is passed through upper and lower electrical heating elements each of which are controlled individually by temperature sensors that, for example, are set to high, medium, or low settings as desired.
As a design feature of conventional water heaters, in order for the water heater to function properly, the water in the storage tank must be periodically heated to maintain the water temperature at the temperature selected for output for household usage (even when no hot water is being used by the household). If the water in the tank is not periodically heated, the water will eventually cool to the ambient temperature due to various standby losses, e.g., heat conducted and radiated through the walls of the tank and/or heat lost through the flue pipe. Moreover, if there is not a pilot-less ignition system, a pilot light must be constantly maintained so that the burners can be fired up when needed such as, for example, when cold water enters the storage tank as hot water is being used by the household. As standby losses represent approximately 10% to 20% of a household's annual water heating costs, it can be seen that alternative water heating devices which do not operate with such high energy loss rates (e.g., due to standby losses) are desirable.
An alternative type of water heater which does not suffer the above-described standby losses known as a tankless or a demand-type water heater (hereinafter simply referred to as a “tankless” water heater), is recently gaining in popularity in the United States. Specifically, as their name would indicate, tankless water heaters do not utilize water storage reservoirs. Instead, tankless water heaters sense or detect when hot water is being demanded by the building in which they are installed (e.g., by sensing a pressure drop in the hot water line), and then subsequently, simultaneously, activate a heating device and open a water flow valve in the water heater. Then, water travels through the passageways of the water heater, the heating device heats the water substantially instantaneously to a desired temperature and thereafter feeds the heated water to the plumbing of the building (e.g., household). Heating devices conventionally employed by tankless water heaters utilize electrical resistance or, alternatively, natural or propane gas-fired burners.
As a principle benefit of the design of tankless water heaters, such water heaters only heat water when there is an immediate demand for it and therefore do not employ or require a water storage reservoir. As a result, standby (heat) losses, such as those experienced by storage-tank-type water heaters, are substantially eliminated. Although, as can be seen, tankless water heaters present significant energy efficiency improvements over conventional tank-type water heaters, further improvements in tankless water heater efficiencies are desired. In an effort to address this desire for further improvements, significant efforts have been made in the industry to develop energy efficient water heaters powered by fuel cells. An exemplar listing of patents attempting such improvements is listed and described in brief detail below.
For example, the Yamamoto et al. reference (U.S. Pat. No. 6,420,060) discloses a solid polymer fuel cell water heater cogeneration system requiring the use of a fuel reformer to create hydrogen rich fuel gas. Such a system is impractical for residential use and would increase the size, complexity, and cost of the water heating system because hydrogen rich fuel gas is necessary for operation of the device (as well as for all known polymer fuel cells). Furthermore, the disclosed system requires the use of a storage tank for storing heated water and, therefore, experiences standby losses associated therewith.
In another example, the Hsu et al. reference (U.S. Pat. No. 6,054,229) discloses a system which integrates a fuel cell energy system with a Heating, Ventilation and Cooling (HVAC) system.
In still another example, the Crownden et al. reference (U.S. Pat. No. 6,645,652) discloses a fuel cell based electrical power generation system including a water circulation subsystem for circulating water within a fuel cell system and a water reservoir for collecting recycled water. The '652 reference further discloses a cogeneration heat exchanger associated with a temperature control subsystem for transferring thermal energy from the fuel cell system to a cogeneration system external to the fuel cell based electrical power generation system.
Although the above delineated references have in some instances, attempted to make improvements in cost or energy efficiency when compared to conventional storage tank-type and tankless water heaters, none of the references discussed, addressed or solved all of the drawbacks described above.
In view of the above-enumerated drawbacks, it is apparent that there exists a need in the art for apparatus and/or methods which solve and/or ameliorate at least one of the above problems of prior art water heaters. It is a purpose of this invention to fulfill these needs in the art as well as other needs which will become more apparent to the skilled artisan once given the following disclosure.